(662d) Continuous on-Demand Synthesis of Perovskite Quantum Dots

Metal halide perovskite quantum dots (QDs)^1,2 have rapidly grown to become one of the most promising classes of nanomaterials for applications in low-cost and highly efficient optoelectronic devices. Anion exchange reactions of the highly luminescent perovskite QDs provide a facile post-synthetic route for on-demand tuning of the absorption/emission bandgap of perovskite QDs. Conventionally, synthesis, screening, and optimization of colloidal QDs are conducted using the time- and material-intensive flask-based approaches. Discovery and optimization of QDs is therefore limited by the sampling rate, off-line analysis time, and batch reactor/reaction process control. Batch reactors suffer from inefficient mixing and heat transfer rates that degrade the resulting optical properties of the QDs.

Our group has recently developed a modular intelligent flow reactor integrated with a translational in situ spectral monitoring probe for continuous synthesis and systematic studies of the colloidal synthesis and anion-exchange reactions of perovskite QDs.^3-5 Utilizing the developed flow synthesis platform, we have demonstrated, for the first time, a mixing-controlled growth kinetics of cesium lead tribromide perovskite nanocrystals. Varying the average droplet velocity moving in the flow reactor, tunes the degree of QD precursor mixing within droplets, resulting in perovskite nanocrystals with different optical properties.

In this work, we present a facile room-temperature anion exchange strategy for rapid bandgap tuning of inorganic perovskite QDs using a modular flow reactor. The automated QD synthesizer platform consists of modular heating units, a novel in-line micromixer, and a unique in-situ translational flow cell (UV-Vis absorption and fluorescence spectroscopy). The translational movement of the spectral monitoring probe along the tubular reactor decouples the effect of early timescale mixing of QD precursors from the residence time (i.e., growth time) along the microreactor. Automated sampling along the continuous flow reactor enables rapid photoluminescence and absorption spectra sampling across 75 ports (i.e., unique reaction times) spanning residence times ranging four orders of magnitude.

The developed flow synthesis approach enables rapid discovery, screening, and optimization of perovskite QDs with desired optoelectronic properties via high-throughput screening (>500 experimental conditions per day) of the accessible QD synthesis parameter space.

(1) Akkerman, Q. A.; Rainò, G.; Kovalenko, M. V.; Manna, L. Genesis, challenges and opportunities for colloidal lead halide perovskite nanocrystals. Nature Materials, 2018, 17, 394-405.

(2) Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V. Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut. Nano Letters, 2015, 15, 3692-3696.

(3) Epps, R. W.; Felton, K. C.; Coley, C. W.; Abolhasani, M. Automated microfluidic platform for systematic studies of colloidal perovskite nanocrystals: towards continuous nano-manufacturing. Lab on a Chip 2017, 17, 4040-4047.

(4) Epps, R. W.; Felton, K. C.; Coley, C. W.; Abolhasani, M. A Modular Microfluidic Technology for Systematic Studies of Colloidal Semiconductor Nanocrystals. Journal of Visualized Experiments, 2018, e57666.

(5) Abdel-Latif, K.; Epps, R. W.; Kerr, C. B.; Papa, C. M.; Castellano, F. N.; Abolhasani, M. Facile Room-Temperature Anion Exchange Reactions of Inorganic Perovskite Quantum Dots Enabled by a Modular Microfluidic Platform. Advanced Functional Materials, 0, 1900712.